1. Field of the Invention
The present invention relates to an image processing device operable to improve deterioration in image quality that may occur at scene change of images, an image display device using the image processing device, and an image processing method to be practiced in the image processing device.
2. Description of the Related Art
Thanks to the development of information-oriented society, people can easily send and receive not only character information and speech information but also image information with a personal computer and a cellular phone.
In video devices that send and receive the image information, high quality image display on the image display device has been pursued in order to display finer images.
One of the methods for attaining high quality image display is performing image quality correction to an image signal for every frame.
In the method, if correction for brightness value and chroma value of the image signal is often performed, flickering due to the correction can occur when the image signal is displayed on the image display device. The prior art employs technique that slows down temporally the correction, as slow as people can not perceive the correction, so that the flickering is suppressed.
However, when a scene is switched to change the image signal greatly frame by frame, over-suppressed correction may fail in performing desirable swift correction, resulting in a correction gap in the course of correction and hence in deterioration of image quality.
In order to solve the problem, in Published Japanese Patent Application Laid-Open No. 2002-262303 (reference 1), a scene detecting means operable to detect a scene change of an image signal (for example, switching of displayed scenes) is provided, so that change amount of correction is controlled, thereby suppressing the flickering and the correction gap.
In the following, an image quality correcting method according to the prior art, as represented by the reference 1, is explained.
FIG. 17 is a block diagram of the prior image correction device. The prior image correction device comprises a correcting unit 1, a target correction amount calculating unit 2, a change amount controlling unit 3, and a scene change detecting unit 4.
In FIG. 17, the correcting unit 1 performs image quality correction to an input image signal that is inputted into an input terminal 5, and outputs the corrected image signal to an output terminal 6 as an output image signal. At this time, the change amount controlling unit 3 calculates a correction amount of the image quality correction that is mentioned above, based on a target correction amount that the target correction amount calculating unit 2 has calculated, and detected result of the scene change detecting unit 4. The scene change detecting unit 4 is provided in order to detect a rapid change of a scene (for example, scene switching). The change amount controlling unit 3 suppresses flickering and a correction gap by calculating the correction amount that the correcting unit 1 uses, based on the correction amount to the present scene and the correction amount according to the scene change.
FIG. 18 shows relationship between the input change amount and the output change amount in the prior image correction device. In the prior image correction device, a curve 8 defines the relationship between the input change amount and the output change amount. Especially when the input change amount is located between a point P and a point Q, the output change amount is set as a constant value R. Thus, flickering of the screen due to the rapid scene change can be prevented.
However, since the prior scene change detecting method detects only the occurrence of the scene change and performs image quality correction by the detected result, image quality correction considering the magnitude of the scene change can not be performed, and a high-performance image quality correction can not be performed, either.
In detecting the scene change, if so-called false detection occurs, such that a scene change detecting signal is not sent even though the scene has actually changed and that a scene change detecting signal is sent even though the scene has not changed, a gap between the correction change amount and the actual change amount becomes significantly great; therefore, deterioration in image quality occurs.
Even if an advanced scene detecting method is used, it is difficult to conquer such false detection completely.